In general, it is state of the art in technology to join internal sheets and external sheets by flanging. This method calls for high dimensional accuracy of those components to be joined and it might be required to take additional measures, e.g. applying an adhesive to obtain a lasting connection.
EP 200 997 B1 discloses a welded connection of two light-gauge sheets, of which one external sheet forms an optically smooth exterior surface, the edge of which is flanged by 180° onto its rear area, and wherein the internal sheet is laid onto the flanged edge of the external sheet, and wherein the connection of the internal sheet with the flanged edge is made by a laser beam from the side averted from the exterior surface. In addition, the internal sheet in the edge area can also be flanged by 180°.
EP 855 965 B1 discloses a motor vehicle door with an internal sheet and an external sheet, wherein the edge strips of the internal sheet and of the external sheet are bent and wherein the edge strips of these sheets laid one above the other are welded together by a laser beam directed into the gap between the two edge strips. The vertical bend at the entire circumference of the sheets with the smallest possible joining gap involves a sophisticated box-like stacking and positioning of the components to each other. The gap which is required for box-like stacking is then formed between the sides lying opposite to each other, thus constituting the joining gap. The required component tolerances can hardly be met in deep drawing. It is also disadvantageous that the gap cannot be influenced any more by shifting the inner part. The gap can only be reduced by deformation of the external sheet, whereby the strains and stresses thus occurring may affect the outer skin and produce dips.
DE 100 37 303 A1 describes a method for producing a motor vehicle door, wherein the door inner part is entirely or partly made of aluminum and the door external sheet is completely made of aluminum. According to this method, the edge area of the door external sheet at the entire circumferential area is inwardly bent by approx. 90° and brought in contact at a machined front area of the door inner part to allow for executing the laser welding operation. In producing this door, too, positioning and box-like stacking is difficult, leading to the a.m. problematic situation concerning tolerance, gap, and dips.
Furthermore known from DE 199 32 415 C1 is a method according to this species for laser beam welding of a motor vehicle door or motor vehicle damper, wherein the edges of the sheets to be joined are inwardly bent in the same direction at the entire circumference of the door and wherein the sheets are welded together in the edge area of the edge strips, maintaining a certain space for degassing. With this method, too, a uniformly thin joining gap must be established at the entire circumference, involving substantial expenditure for laser welding.